Most child restraint systems are currently designed to be fitted in a vehicle seat and secured to it by using a vehicle's adult lap and diagonal seat belt, or sometimes just the lap belt. However, vehicle seats, seat belts and their anchorages vary greatly between different models of vehicles; the seats have different shapes, the seat belts may be shorter or longer, the position of the anchor points differs etc. All these factors make it virtually impossible to make a child restraint system that fits in all vehicles and this sometimes make it complicated or even impossible to fit the child restraint system correctly.
A child restraint system is described in GB 2.417.416. The system comprises a body having a base portion and a seat portion which comprises adjustable restraining means for securing a child passenger therein, The seat portion is connected to the base portion via seat mounting means and is capable of movement relative to the base portion in a direction that is consistent with the direction of vehicle travel. The base portion includes anchor means for fixing the body to the interior of the vehicle, an energy absorbing apparatus for absorbing some of the energy generated during a vehicle collision, and a regulator coupled to the adjustable restraining means such that adjustment of the adjustable restraining means also results in adjustment of the amount of energy absorbed by the energy absorbing apparatus during a vehicle collision.
U.S. Pat. No. 5,685,603 describes a child seat located on rails. The slide rails are fixed at both ends to the body of the vehicle. The seat can slide along the rails during a collision and the force of the collision is separately absorbed by a variety of energy absorption means.
US 2009/0273215 discloses a child safety seat for installing a baby on a vehicle sea. where the safety seat comprises a seat structure and an intermediate structure providing the connection between the seat structure and a standard anchor unit associated with the vehicle seat.
U.S. Pat. No. 7,488,034 discloses a child safety seat assembly. including a base for being positioned on a vehicle seat bottom. An anti-rebound bar is carried by the base and extends outwardly and upwardly from a foot end of the base for engaging a seat back of the vehicle to which the seat is attached for retarding inertia-induced rotation of the base and the attached carrier by transmitting rotational force applied to the seat during a sudden change in velocity into the seat back of the vehicle seat onto which the seat is attached.
U.S. Pat. No. 7,328,946 discloses a chassis which is suitable for supporting a child vehicle seat, where the chassis is provided with a frame and connectors that can be detachably connected in use to securing elements that are present in a vehicle. The chassis is further provided with an unlocking mechanism for releasing the engagement between the connector and the securing element.
U.S. Pat. No. 7,044,549 discloses a child safety seat, where the child safety seat comprises a seat structure having a base support for resting on a vehicle seat cushion and a seating surface for a child occupant. A rigid link is attached to the child safety seat structure solely by a coupling mechanism that permits angular movement of the child seat structure relative to the rigid links about an axis located above the base support surface. A releasable connector is mounted on the rigid link for engagement with a standard anchorage unit associated with the vehicle seat.
Based on the above mentioned compatibility problems, there has arisen a need for a standard system for fitting a child restraint in a vehicle. In an attempt to standardize the securing of a child restraint to a seat assembly for a vehicle, seat assemblies have been modified to accomplish this means. In particular, anchorage points in the form of loop fasteners are secured to a frame of the seat assembly, between the seat cushion and the seat back. These loop fasteners are commonly referred to as ISOFIX steel bars (ISOFIX stands for “International Standards Organisation FIX”). A latch mechanism in the form of latches or clips extending out from the bottom of the child restraint engages the loop fasteners to provide a positive attachment of the child restraint to the seat assembly.
However, if a vehicle with an ISOFIX system is involved in a vehicle crash, where the vehicle, due to the crash, is exposed to sudden deceleration, the forces involved will try to rotate the child restraint about the anchorage points. This will occur since the mass centre point of the child restraint and the child are located above the anchorage point. The child restraint will then rotate either downwards into the vehicle seat or upwards towards the roof of the vehicle, depending on whether the collision is from the behind or from the front. In both cases the rotation will result in that the child is moved. As a child's head is relatively heavy compared to the rest of the body, it is desirable to reduce the head displacement of the child to a minimum in order to protect the child from severe injury.
In order to solve this problem several technical solutions have been proposed. One idea includes the introduction of a third anchorage point, such as a top tether connecting a back portion of the child restraint to the vehicle seat, or a floor support to minimize the rotation of the child restraint during sudden deceleration.